I know I'm probably stupid but I've asked stupid questions my entire life and I'm not going to stop now.  Every time I walk down by the Boise River I see this stuff all over rocks and trees.  What is it?

Credit: Rick and Carly / Townsquare Media

It looks like some kind of a greenish moss or mold with white in there.  It has a flower type shape to it and looks like it spreads.  Is it poisonous or hazardous to anyone walking by?  I seriously doubt someone's going to eat it but what if you're taking your dog for a walk along the Green Belt and you know how dogs are... they grub down just about anything.  Should I be worried if this happens?

I've searched Google and YouTube and I keep coming up with about 400 different possibilities of what this is.  Can anyone narrow that down for me and give me a little info?  I'll trade you Boise Music Festival tickets for knowledge.  Ha!  Thank you in advance.